Spring is just around the corner when it will be time to stop using the open fire and woodburning stove, but before you forget not only is now the best time to have you chimney cleaned, to prevent the risk of a soot fall or to help extend the life of your stainless steel liner. (Phone ProSweep on 01626 830251 now to book your sweep), but also is the time to organise your firewood for next winter.
Choosing Logs
When choosing wood for burning there are two significant factors which have an effect on the net calorific value (CV) or the amount of available heat per unit (volume) of fuel:
1. Moisture Content
2. Wood Density
Moisture Content
The moisture content of wood has the greatest effect on net Calorific Value (CV). Any water in the timber has to evaporate before the wood will burn, and this will reduce the net energy released as useful heat (as opposed to steam up the chimney). Logs that aren’t dry will result in a fire that smoulders and creates lots of tars and smoke. These tars can be corrosive, potentially damaging the lining of the flue and increasing the danger of a chimney
Fire. Wet logs will tend to blacken glass in stoves even if the stove is designed to keep the glass clean. Well seasoned logs can have approximately twice the CV of green logs. Always burn dried (seasoned) wood, either by buying it dry, or by buying green logs and drying them yourself. Radial cracks and bark that comes off easily are signs of well-seasoned wood.
Wood Density
When buying logs, it is common for the seller to let you know whether they are from hardwood or softwood tree species (or mixed). The general difference is that hardwoods (deciduous, broadleaved tree species) tend to be denser than softwoods (evergreen, coniferous species). This means that a tonne of hardwood logs will occupy a smaller space than a tonne of softwood logs. Dense woods will burn for longer than less dense woods, this
means you will need fewer ‘top ups’ to keep a log stove burning. If you buy wood by volume you will receive more kilowatt hours (kWh) of heat from a cubic metre (m3) of hardwood than softwood (at the same moisture content).
Softwoods are easier to light and often cheaper to buy however.
How to Dry Your
Own Logs
• Green logs are considerably cheaper to buy than seasoned logs, but will be heavier and will require space to stack and dry before use.
• Timing of felling is important as standing timber will be driest in winter. Many manufacturers often specify 20%
Moisture content or less, and this is likely to take two summers or more to be achieved by air drying.
• Drying timber should be stacked on bearers (off the ground) in a sunny, windy location, ideally under some form of waterproof cover with open sides. Ideally the prevailing wind should blow through the stack. If possible, cross cut logs should be split to less than 10cm diameter. This allows moisture to move from the centre of the log to the surface more easily.
• To achieve low moisture content for burning, bringing cut, split logs indoors for a few days or more before use
Contamination
Do not burn anything that has been contaminated or treated with paint, varnish or other coatings and preservatives. Contamination can affect the amount of tar and deposits building up in your chimney, and release noxious chemicals into the smoke. Contaminated wood often leaves melted debris in the ash, and can have serious health implications when burnt. In particular, old treated (tanalised) wood contains arsenic and should never be used as fuel.